The Stovebolt Site Forums The Shop Area General Truck Talk 1951 half ton w/ 216 - radiator leaking at start up?

High all and happy holidays.

I have a quick question. Anybody have trouble with radiator leaking at start up?

When I first start the 51 up (1951 1/2 ton Chevy with original 216)as it warms up before the thermostat opens,it pushes anti-freeze out the overflow. I have a 0 lbs. cap on the radiator now. I tried a 4 lbs. cap before I got the new one (0 lbs.)and I would get a leak on the drivers side of the block until the engine warmed up. After the engine warmed up it wouldn't leak any more.

The engine was rebuilt by previous owner but was nerer started. Everything is alright after the first time the thermostat opens, no more leaks.Any sugestions on what is hapening here?

Thanks in advance.

Those motors aren't supposed to leak at the block at any time. I would check for a cracked block. It could be a freeze plug leaking or the water pump. Check your oil for antifreeze also.
Will the radiator leak every time or just when you refill it? It may be just seeking it's own level. It could be a cracked head that is pressurising the radiator. Will it overflow without a cap on it? Check for bubbles in the radiator this could confirm a cracked head.
Not very good news but I hope this helps.
Tom

No water in the oil,no bubbles in the radiator and I can't tell were it is leaking, just 2 or 3 drips on the floor, from drivers side under the alternater(with the 4 lbs.cap)then it stops as soon as the thermostat opens.NO more leaks after it warms up to operating temp.

elm,

So you have two ongoing problems. It always leaks a few drops and the radiator always bubbles over when warming up...is this right, or did both these things happen ONCE and now all is well.

Stuart

Ongoing problem.After it warms and thermostst is open it will run all day and never overheat or leak.It will only leak at first start up. It has a new thermostat 160 degrees and it also did it when it had a 180 degree thermostat.

elm,

Leaks happen...try to find it if you can. It could be a loose clamp or loose pipe fitting. A cold engine under pressure, before the thermostat opens would be the prime candidate for a 'little dripper'. Even a head gasket could do it. If it is a leak that can't be stopped by re-gasketing or tightening, then a sealer is not a sin! A tiny can of Alum-seal certainly won't bring the sky crashing down.

I would stick with the 160&deg thermostat, but I would drill a small hole in the flange near the edge. This probably won't hurt anything and might give the coolant a little cushion and keep it from hitting the cold radiator when the thermostat does open.

Stuart

Try and tork the head bolts, I had a small leak around one on the left front. When we put the engine back in we had a chain on the front head bolt ans forgot to retork it after we took off the chain.

Well my first thoughts are these: One you have too much coolant and second I would pull the thermastat out and dill a small hole in the flange to let air and water pass. Good Luck!

Sometimes that small leak around the gen, comes from the upper gen arm to block bolt. This bolt goes all the way into the water jacket and needs some sealer put on it.

Brian;
What size hole do you recomend I drill in the thermostat? Thanks for the replies.

elm
Something small. No larger then an 1/8 but I would gofor something like 3/32. Make sure that the hole isn't covered by the gasket.

I was thinking about this some more after I posted. You say it only leaks at start up. Question, are you driving it after start up or is it sitting in the drive way? If you are driving it. It may still be leaking and it may not be noticable because it is being blown away. If it is sitting in the drive and not leaking after the therm opens I would still check the coolant level.

My 49 leaks from the water pump seal just a little at start up and then it stops. I know it will go to full out leaking all the time but I keep a close eye on it.

Brian;
It is still sitting in the garage. Not road ready yet. I just start once in a while to keep battery charged up.I am going to try to get to work on it Friday.I will check bolts and put sealant on them and I am going to drill the hole in thermostat. We will see what happens then. Again thanks for the help.

I think I would live with it for a few cold/hot cycles. You may be topping it off each time and it doesn't want to be all the way to the neck. I had a flathead that would do that and as it turned out 3/4 of the top tank was all it wanted. As the coolant expands it has to go somewhere. See if after a few cycles it stops spitting.

first thing to notice is that the rad ahould only be filled when up to operating temp, and rad should only be filled to an inch below the neck max - as Slo sez, quit topping it up and it'll be fine

Bill

I have a car like that...3/4 full is all it will take. I wondered about the water pump too, but that would continue to leak if bad wouldn't it? I did replace a water pump on a old truck and the leaking stopped, but b4 that when running or after parking it dripped...

Finally got back to the 51 yesterday. I pulled the thermostat and drilled a 3/32 hole in it and put it back together with the 0 lbs. cap. I didn't add any coolant to it this time and left it down about an inch from the top. So far so good. No leaks. Didn't heat up either. Thanks to all who helped.

I don't think it can be an overfill problem cause woundn't that show up when it gets hot? As it drys up when hot, that implys something that is leaking is getting hot and expanding to close off the leak. I would go more for head bolts and the generator bolt to make sure they are tight. But, if the leak is cured, then great! Good luck.

Bad news. I took the left front fender off to start on the wiring harness and started the 51 just to let it warm up. I was watching to see if it leaked any more and sure enough it did. I finally found my leak. The block is cracked. It has a 3 inch crack on the #3 cylinder. Too bad the motor was rebuilt by the previous owner. I am on the look out for a 216 if i can find one, or how many parts off the 216 will fit a 235? Any body in the Wisconsin area have a good 216 or a 235 that you want to let go? Any help will be appreciated.

there will be expanson of the coolant as it warms so keep level in radiator just above the core tubes,,,,any leaking anywhere isnot correct and should be corrected...doc

Is the crack horizonal near the bottom of the water jacket? If so, it is likely a freeze crack and will not get any worse. I would just clean it well, vee it out alittle with a grinder and repair it with JB Weld. Texture it while soft with a piece of 40 grit sandpaper pressed into the epoxy and it will look OK.

That should hold it fine until you find another engine, or it will probably be leakfree for the rest of it's life, maybe yours too.

Nope the crack is vertical about 2 inches up from the oil pan flange. Straight up the block from top to bottom.

Eric,

Sorry to hear of your mis-fortune with that cracked block!

Sure wish you were closer. I've got a spare 235 sitting in the garage, looking to be used.

You'll probably be able to find something out there. I went through the same experience with my 46. Found a guy nearby that was "rodding" a 39 coupe. Bought his fully rebuilt entire drive-train for $250. Good Luck with the search.